1. Field of the Invention
This invention relates to non-thermal electron-induced reactions of Group V hydrides with a surface layer produced by adsorption of Group III metal alkyls on an inert surface. The atomic hydrogen (H) produced by electron-induced dissociation of Group V hydrides to form the species (Group V) H.sub.x and H, efficiently extracts the alkyl groups from the Group III metal alkyl layer leading to chemical activation and to carbon removal from the Group III-V compound semi-conductor film which is formed. More particularly, the invention relates to a method of synthesizing a GaN compound semi-conductor film from trimethylgallium (TMG) and ammonia.
2. Description of the Prior Art
The III-V compounds, in particular the wide band gap nitrides, are very attractive semi-conductors for light emission applications in the blue and UV wavelengths at high temperatures. [S. Strite et al., J. Vac. Sci. Technol. B. 10, 1237 (1992).] The effort to produce high quality films of Group III-V compounds can be traced back to the 1960's where much work was initiated in an attempt to better understand compounds such as GaN, InN, and AIN. The earliest GaN samples studied were in the form of powder samples or small crystals. [W. C. Johnson et al., J. Phys. Chem, 36, 2651 (1932).] The most prevalent technique for producing these nitride compounds was to place metallic Ga in a zone furnace and to flow NH.sub.3 over it, [W. C. Johnson et al., J. Phys. Chem, 36, 2651 (1932)] or to use a gallium phosphide or gallium arsenide, [A. Addamiano, J. Electrochem. Soc., 108, 1072 (1961)] or a gallium subchloride source for transport of Ga into the furnace. [H. P. Maruska et al., Appl. Phys. Lett., 15, 327 (1969).] Another common growth technique was the use of reactive sputtering. This method employed Ar ions to sputter a Ga film in the presence of a nitrogen plasma. [H. J. Hovel et al., Appl. Phys. Lett., 20, 71 (1972).] The GaN produced by these methods was suitable to investigate and characterize many of its properties; however, material good enough for electronic applications was still elusive. Heteroepitaxial growth was finally realized by the use of chemical vapor deposition (CVD) techniques. [S. Strite et al., J. Vac. Sci. Technol. B. 10, 1237 (1992).] This permitted the production of high quality films where the principal problems dealt with finding suitable substrates for a good lattice match, elimination of very high background n-type carrier concentrations thought to be due to nitrogen vacancies, and the incorporation of dopants. The problem of a proper substrate lattice match that is also thermally compatible with the GaN thin film has been investigated by the use of substrate materials such as SiC, ZnO, and MgO. [S. Strite et al., J. Vac. Sci. Technol. B. 10, 1237 (1992).] The production of stoichiometric GaN is still a major obstacle for producing electronic grade films. Lower growth temperatures that might allow better nitrogen incorporation from more reactive nitrogen-containing precursors are being considered. [H. Okumura et al., Appl. Phys. Lett., 59, 1058 (1991); M. Rubin et al., Appl. Phys. Lett., 64, 64 (1994).]
The growth of the III-V nitrides, in thin film form using metal organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE), is now widespread and many variations of these two techniques are in use and are just beginning to be understood. In particular, the thermal decomposition of trimethylgallium, Ga(CH.sub.3).sub.3, (TMG) in the presence of NH.sub.3 can be used for GaN film production. [A. F orster et al., J. Vac. Sci. Technol., B7, 720 (1989).] However, this type of process is known to leave carbon behind, which can be deleterious to III-V semi-conductor films [T. R. Gow et al., Vacuum, 41, 951 (1990); C. R. Flores et al., Surf. Sci., 261, 99 (1992); T. R. Gow et al., J. of Crystal Growth, 106, 577 (1990); and S. P. Den Baars et al., J. Cryst. Growth, 77, 188 (1986)].
Therefore, there remains a very real and substantial need for a method and apparatus working at low temperatures that forms very pure Group III-V compound semi-conductor films, wherein carbon is efficiently removed, particularly wide band gap nitrides, for light emission applications in the blue and UV wavelengths.